Laser-induced thermal transfer processes are well-known in applications such as color proofing and lithography. The processes use a laserable assemblage comprising a donor element that contains the imageable component, i.e., the material to be transferred, and a receiver element. The donor element is imagewise exposed usually by an infrared laser resulting in transfer of material to the receiver element. The exposure takes place only in a small, selected region of the donor at one time, so that the transfer can be built up one pixel at a time. Computer control produces transfer with high resolution and at high speed.
For the preparation of images for proofing applications, the imageable component is a colorant. For the preparation of lithographic printing plates, the imageable component is an oleophilic material which will receive and transfer ink in printing. In general, these materials do not absorb at the wavelength emitted by the infrared laser. Thus, in most cases a separate infrared radiation absorber is also included.
"Back transfer" can be a problem in the preparation of multicolor images using laser-induced thermal transfer processes. When a second color is applied to the receptor, some of the first color already on the receiver is transferred back to the second donor element. This results in lower color density and poor uniformity. In the preparation of lithographic printing plates using laser-induced thermal transfer processes, the durability of the transferred oleophilic coating can be a problem. The material wears off and does not last for the large number of copies required for lithographic printing runs.